HR: 16:15h
AN: A54B-02    [Abstracts]
TI: Impact of Aerosol-Cloud Interactions on Tropospheric Ozone
AU: * Unger, N
EM: nunger@giss.nasa.gov
AF: NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, United States
AU: Menon, S
EM: smenon@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS90KR109, Berkeley, CA 94720, United States
AU: Shindell, D
AF: NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, United States
AB: Aerosol-cloud interactions may impact tropospheric ozone (O₃) directly through modifications to photolysis rates and washout of precursors and indirectly through changes in climate variables such as temperature. Most previous studies of past and future O₃ changes have neglected the influence of aerosol-cloud interactions. We apply the NASA Goddard Institute for Space Studies model for Physical Understanding of Composition- Climate INteractions and Impacts (G-PUCCINI) to quantify the impact of aerosol-cloud interactions on O₃ radiative forcing and surface air quality for the 2030 A1B future atmosphere relative to 1995. Aerosols simulated include sulfate, organic carbon, black carbon, sea-salt and dust. The aerosol-cloud interactions simulated for liquid-phase stratus and cumulus clouds include (1) the first aerosol indirect effect: increased (decreased) cloud reflectivity due to an increase (decrease) in aerosols and cloud droplet number concentrations and reduced (increased) droplet sizes: and (2) the second aerosol indirect effect: change in cloud cover, cloud liquid water path and precipitation due to smaller droplet sizes that inhibit precipitation processes. For 2030 relative to 1995, the aerosol indirect effect is -0.69 Wm-2 mainly due to increases in cloud liquid water path at the expense of suppressed precipitation leading to increases in cloud optical depth. The global annual mean O₃ radiative forcing across this time period is +0.126 Wm-2, 10% less than for experiments that do not consider aerosol-cloud interactions. Our results imply that aerosol-cloud interactions have limited the O₃ forcing since the preindustrial. When aerosol-cloud interactions are included, simulated surface O₃ at 2030 is decreased across the United States and South Asia and increased across Europe, around 1-2 pbbv on the annual mean. We use the model to explore the effect of the observed global decrease in reflective aerosol since 1990 on tropospheric O₃ despite the counteracting influence of air quality control legislation on O₃ precursors in the United States and Europe, and the simultaneous decline in the methane growth rate across the same time period.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0321 Cloud/radiation interaction
DE: 0365 Troposphere: composition and chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 3311 Clouds and aerosols
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting